Methods of and apparatus for grit blasting



Nov. 3, 1959 A. J. BRUNNER METHODS OF AND APPARATUS FOR GRIT BLASTING Filed Jan. 13, 1956 United States Patent METHODS OF AND APPARATUS FOR GRIT BLASTING Anton J. Brunner, Congress Park, 111., assignor to Western Electric Company, Incorporated, New York, N. a corporation of New York Application January 13, 1956, Serial No. 558,964

1 Claim. (Cl. 51-282) This invention relates to methods of grit blasting, and more particularly to methods of blasting With moist black walnut shell grit.

In the use of black walnut shell grit to blast molding flash and irregularities from molded parts, such as molded portions of Wire spring relay combs, the grit powders as it is used and becomes unsuitable for further blasting operations. Also, if the grit is dry it is lighter and has less blasting impact than if moist and tends to accumulate static charges which cause some grit particles to stick to parts being blasted. It has been proposed in the past to moisten the grit, but no methods or apparatus were known which would moisten the grit sufficiently without caking the grit so that it clogged the apparatus.

An object of the invention is to provide a method of moistening blasting grit.

Another object of the invention is to provide a method of moistening blasting grit sufficiently to prolong the life of the grit.

In a method illustrating certain features of the invention, hot steam condensate is sprayed on a sheet of blasting grit to moisten the grit and then the grit is blasted against articles to be cleaned.

In a method forming a more specific embodiment of the invention, black walnut shell blasting grit is propelled by streams of air against articles to be cleaned, and is elevated and dropped against a deflector which drops the grit in a sheet past a plurality of atomizing nozzles leading from a condensate trap of a steam line. The steam forces the condensate through the nozzles, which sprays hot condensate in a fine mist against the falling sheet of grit to moisten the grit thoroughly, after which the cycle is repeated.

A complete understanding of the invention may be obtained from the following detailed description of a method forming a specific embodiment thereof, when read in conjunction with the appended drawings, in which the single figure is a partially sectional view of an apparatus for practicing a method forming one embodiment of the invention.

Referring now in details to the drawing, there is shown an apparatus for applying steam condensate at a temperature somewhat below the boiling point, preferably in the order of 170 F., to black Walnut shell blasting grit 10, preferably of a particle size of from 0.016 inch to 0.028 inch in diameter, as the grit is dropped in a thin sheet or curtain 11 from a chute 12 past a row of atomizing nozzles 13 of a well known type directed at the sheet 11'. The nozzles 13 are supplied with hot steam condensate from a supply pipe or header 14 leading from a condensate pipe 16 connected at its upper end to and forming one end of a steam line 17 leading from a source of steam under pressure. The steam line has an adjustable reducing valve 18 therein which condenses the "ice steam to water in the pipe 16. An overflow line 19 leads to an adjustable condensate trap 20 and drains all condensate from the pipe 16 above a point 21 thereon. A suitable steam pressure has been found to be about ninety pounds per square inch in the line 17 reduced to about seventy pounds per square inch in the pipe 16.

The hot condensate is continuously blown, by the pressure of the steam, in a fine mist against the continuously dropping sheet 11 of blasting grit, and the hot condensate soaks into the grit particles to give them resiliency. The moisture added should be about ten percent of the weight of the grit, and may be regulated by the reducing valve 18. The particles drop from the chute 12 in a uniform quantity per unit of time which is regulated by an elevator (not shown), or the like, feeding the grit from the bottom of a grit blasting chamber positioned directly below a hopper portion 22 of a moistening chamber 23. The constant steam pressure supplies a uniform quantity of condensate per unit of time to the curtain or sheet of grit, which absorbs all the condensate blown from the nozzles. The moistened grit travels from the hopper portion 22 directly to grit-blasting nozzles. The nozzles 13 cover the sheet so that the condensate is applied substantially uniformly from one edge of the sheet or curtain to the other and the grit tumbles down into the hopper 22. The nozzles 13 are directed downwardly as well as toward the sheet so that: any mist missing the curtain strikes a pile of grit in the hopper portion. Then the grit is sucked to blasting nozzles (not shown) and is blasted against articles. The grit then is collected, elevated and again dropped into the chamber 23.

The above-described method and apparatus thoroughly moistens the grit with the hot condensate which penetrates into the body of each particle and thus renders it resilient. Since the moisture does not collect on the exterior of each particle, there is no clogging of the apparatus from such moisture. Also, since all the spray from the nozzles is water, any portion traveling beyond the sheet falls on the grit at the bottom of the chamber and does not strike the walls of the chamber and wet the walls.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

The method of blasting with walnut shell grit comprising continuously dropping such grit in a sheet along a predetermined path, continuously directing a mist of steam condensate at a temperature of about F. on the sheet of walnut shell grit to impregnate the walnut shell grit with steam condensate to cause the shell grit to swell, and removing the swelled moistened grit and blasting it against articles to be cleaned.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,411 Timoney May 2, 1933 2,254,867 Bonotto Sept. 2, 1941 2,278,701 Karr Apr. 7, 1942 2,366,763 Wieland Jan. 9, 1945 2,534,282 Lupo Dec. 19, 1950 2,576,008 Gladfelter Nov. 20, 1951 2,622,047 Ayers Dec. 16, 1952 2,667,015 Berg Jan. 26, 1954 

